Diversification of the country's energy supply is an important aspect of the national energy policy, and the renewable bioenergy will be one of the main energy sources for use in the world's future energy structure. As a new biofuel, butanol has huge market potential with the perfection of upstream and downstream engineering technology for acetone-butanol fermentation industry.
Butanol (n-butanol and 1-butanol) is a four-carbon primary alcohol, with molecular formula of C4H9OH and molecular weight of 74.12. Butanol is a colorless liquid with a distinct odor, and its vapor exerts an irritative effect on mucous membranes and has anesthetic effects at high concentrations. Butanol is mainly used for manufacture of plasticizers such as dibutyl phthalate and aliphatic dibasic acid butyl ester, and is widely used for manufacture of a variety of plastic and rubber products. Butanol can also be used to produce butyraldehyde, butyric acid, butylamine and butyl acetate, which can be used as solvents of resins, paints and adhesives and can also be used as extractants of oils and fats, drugs and spices and additives of alkyd resin paints. In addition, butanol is also a new biofuel with tremendous potential.
However, there are still many problems with the traditional butanol fermentation industries in terms of large-scale industrial application. Wherein a key problem is the low final concentration of the solvent in the fermentation broth. In the ordinary biological methods for preparing butanol, since butanol has toxic effects on bacteria, the mass concentration of butanol is less than 13 g/L, and the yield of butanol is less than 0.29 g/(L·h), and the output of butanol is less than 25% (by mass), resulting in the total mass percent of the solvent in the fermentation broth less than or equal to 2% accordingly. In order to obtain commercial butanol, it is required to use conventional distillation methods, leading to consumption of large quantities of energy.
In order to solve this critical problem, it is necessary to remove the products of ABE (acetone-butanol-ethanol) from the fermentation broth with an effective method, so as to reduce inhibition on product, thereby enhancing fermentation yield and reducing industrial costs.
Currently, the main techniques for separating fermentation products of ABE include gas stripping (GS), liquid-liquid extraction, pervaporation (PV) and adsorption. Meagher (U.S. Pat. No. 5,755,967) et al. separate acetone and butanol by developing a zeolite membrane filled with silicone rubber according to the pervaporation method. The zeolite membrane has excellent selective adsorption on acetone and butanol relative to the adsorption of ethanol, acetic acid and butyric acid. This patent also reports the thermal analytical method, in which the silicalite is heated to 78° C., and the recovery rate of butanol, acetone and ethanol are 100%, 95.5% and 80% respectively, but there are not reports related to test on solubility of ABE in the elution phase. Qureshi, N. et al. (Qureshi, N. et al, 2005, Bioprocess and Biosystems Engineering, 27(4):215-222) recover biobutanol by the adsorption-desorption method, which is the best recovery process when it comes to energy consumption. DIJK (WO 2008/095896 A1) et al. separate biobutanol using a microporous resin with ultra-high crosslinking degree, however the resin has a certain adsorption capacity for ethanol and acetone, increasing the cost of post-separation process. Arjan Oudshoorn et al. (Arjan Oudshoorn et al, 2009, Biochemical Engineering Journal, 48:99-103) adsorb and separate biobutanol by using a zeolite, and investigate adsorption properties of three zeolites (that is, BV28014, CBV811, CBV901) on biobutanol, however, there are problems that the adsorption capacity of the zeolite on biobutanol is not high and the zeolite also adsorbs acetone and ethanol while adsorbing butanol, resulting in increased cost on separation in later stage. David R. Nielsen et al. (David R. Nielsen et al, 2009, Biotechnology and Bioengineering, 102(3):811-821) recover biobutanol in-situ using a polymer resin and investigate the adsorption property of the polymer resin on biobutanol, but there exists following problems: the resin contacts with the fermentation broth directly, resulting in pollution of the resin; the biocompatibilities of some resins are not good; some resins can absorb the substrate of glucose and fermentation reaction intermediates; the adsorption capacities of some resins are low; although some resins have high adsorption capacity on butanol, they also adsorb a great deal of acetone, ethanol and other substances. Milestone et al. (Milestone, N. B. et al, 1981, J Chem Technol Biotechnol, 31:732-736) desorb butanol from the siliceous rock according to the thermal desorption method in which the siliceous rock is first heated to 40° C. to remove water from the siliceous rock, and then heated to 150° C. to recover butanol with the concentration of butanol in the eluent reaching 790-810 g/L, however, it does not involve report on problems of butanol recovery rate and regeneration method. Das et al. (Das, K. et al, 1987, In: Proceedings 4th European congress on biotechnol, 1: 76-78) realize butanol recovery rate of 60-65%, 75-85% and 75-85% respectively by using 120° C. heated steam through the activated carbon, IRC-50 resin bed and XAD-2 resin bed, wherein the outlet gas is condensed using 0° C. water. In summary, there usually exists two main problems with the current adsorbents for butanol fermentation broth: firstly, the absorption capacity of the adsorbent is low, for example, the absorption capacity is less than 100 mg butanol/g adsorbent; secondly, butanol cannot be desorbed from the adsorbent effectively, resulting in lower overall recovery rate of butanol.